A microphone chip, such as a MEMS microphone chip, has a package in which a microphone is coupled to an electric amplifier circuit for amplifying an output signal of the microphone. The electric amplifier circuit may be configured as an integrated circuit and particularly as an ASIC (application-specific integrated circuit). The microphone is coupled to a sensitive input terminal of the amplifier circuit to apply the output signal of the microphone. The amplifier circuit amplifies the received output signal of the microphone and generates an amplified output signal at an output terminal of the amplifier circuit.
In order to operate the microphone a supply potential is applied to an outer terminal of the microphone chip. The outer terminal may be configured as a bond pad to apply the supply potential. The package of the microphone chip is usually constructed compactly and is cost-optimized so that a direct coupling from the supply bond pad to the sensitive input terminal of the amplifier circuit cannot totally be avoided.
Microphones are often used in devices where the supply voltage is not well-controlled and many other devices use the same supply voltage. Thus, a good PSRR (power supply rejection ratio) is required for the audio band to guarantee no audible distortion due to supply changes. The capacitor of the microphone, such as a MEMS motor capacitor, is only in the range of a few pico Farad. Even a parasitic capacitor having a small capacity can limit the PSRR.
It is desirable to provide an electric amplifier circuit for amplifying an output signal of a microphone where the coupling of a supply potential applied to a bond pad at the package to an input terminal of the amplifier circuit inside the package is compensated as far as possible to improve the PSRR. It is a further concern to provide a microphone chip including a microphone and an electric amplifier circuit for amplifying an output signal of the microphone where a coupling of a supply potential applied to a bond pad at the package of the microphone chip to the input terminal of the electric amplifier circuit inside the package is compensated as far as possible to improve the PSRR.